Jansen J, van Buul-Offers S C, Hoogerbrugge C M, Van Den Brande J L
University Hospital for Children and Youth, Het Wilhelmina Kinderziekenhuis, State University of Utrecht, The Netherlands.
Biochem J. 1990 Mar 1;266(2):513-20. doi: 10.1042/bj2660513.
Two somatomedin-like peptides were extracted from Cohn fraction IV of human plasma and brought to homogeneity: one focused at pH 7.8 and the other at pH less than 5.6. Each consisted of two peptide chains interlinked by disulphide bonds. The basic peptide was identical to insulin-like growth factor I (IGF-I) and had a single cleavage in the C-domain before Arg37 [IGF-I(Arg36cl)]. The acid peptide showed identity with IGF-II, with a cleavage in the B-domain before Arg30 [IGF-II(Ser29cl)]. The effects of these cleavages on the characteristics of binding to type I and type II receptor sites, to binding proteins and to antibodies was studied. Binding of IGF-I(Arg36cl) to antibodies directed against the B-domain or against the AD-domain of IGF-I was the same as IGF-I binding. Thus the cleavage does not influence these antigenic sites. In contrast, binding of IGF-I(Arg36cl) to the type I receptor on human and bovine placental cell membranes was markedly decreased compared with IGF-I binding. Binding to the insulin receptor on human placental cell membranes was slightly diminished, whereas the interaction with specific type II receptors on bovine placental cell membranes was unaffected. There was only a minor influence of the cleavage on the region involved in binding to binding proteins. The cleavage in IGF-II(Ser29cl) diminished binding to antibodies directed against the C-domain of IGF-II, compared with binding of IGF-II itself. Binding to receptors (type I and type II) was changed less profoundly. With 125I-labelled IGF-II(Ser29cl), less insulin was needed in order to obtain 50% displacement of the tracer compared with displacement of 125I-labelled IGF-II. The cleaved form of IGF-II probably has a greater affinity towards the common receptor population than does native IGF-II. Binding to binding proteins was not affected by the cleavage in IGF-II.
从人血浆的Cohn组分IV中提取出两种类生长调节素样肽并使其达到均一：一种聚焦在pH 7.8，另一种聚焦在pH小于5.6。每种都由通过二硫键相互连接的两条肽链组成。碱性肽与胰岛素样生长因子I（IGF-I）相同，并且在C结构域中Arg37之前有一个单一的切割位点[IGF-I(Arg36cl)]。酸性肽与IGF-II相同，在B结构域中Arg30之前有一个切割位点[IGF-II(Ser29cl)]。研究了这些切割对与I型和II型受体位点、结合蛋白以及抗体结合特性的影响。IGF-I(Arg36cl)与针对IGF-I的B结构域或AD结构域的抗体的结合与IGF-I的结合相同。因此，这种切割不影响这些抗原位点。相比之下，与IGF-I结合相比，IGF-I(Arg36cl)与人及牛胎盘细胞膜上的I型受体的结合明显减少。与人胎盘细胞膜上的胰岛素受体的结合略有减少，而与牛胎盘细胞膜上特定II型受体的相互作用不受影响。这种切割对与结合蛋白结合的区域只有轻微影响。与IGF-II本身的结合相比，IGF-II(Ser29cl)中的切割减少了与针对IGF-II的C结构域的抗体的结合。与受体（I型和II型）的结合变化较小。与125I标记的IGF-II的置换相比，用125I标记的IGF-II(Ser29cl)时，为了获得示踪剂50%的置换所需的胰岛素更少。IGF-II的切割形式可能比天然IGF-II对共同受体群体具有更高的亲和力。IGF-II中的切割不影响与结合蛋白的结合。
